In computer systems, for example computer system that using general purpose, multi-core (on die Clip Multi-Processing (CMP)) processor and more specifically, a CMP processor using adaptive power management policies, the processor performance state (P-state) adjusts based on demand. As central processor unit (CPU) utilization decreases, the processor may transition to a lower performance state to conserve power. As the CPU utilization increases, the processor may transition to a higher performance state and may consume more power.
In existing operating systems, a target P-state selection is based on the combination of CPU utilization and the last selected P-state. With a Turbo Mode (TM) capable processor, at the last selected P-state, the processor frequency may increase to a highest frequency available when thermal constraints allow it, the actual frequency at which the processor is running may not always correspond to the last selected P-state. This will result incorrect target P-state selection resulting in undesirable performance degradation.
Advanced Configuration and Power Interface (ACPI) is a power management system that allows a computer operation system to control the amount of power consumed by CPU and peripheral devices of the computer system. In existing ACPI processor which includes P-state information, each selectable core frequency is represented with corresponding control, status, and latency information. A replacement of the highest frequency of the last selected P-state with a TM frequency may result in, an increased usage of additional processing power when not needed. Furthermore, this may result in performance degrading caused by P-state fluctuations due to unnecessary transitions to TM.
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